System and method for diagnosing a fluid status of a patient

ABSTRACT

A system and method for diagnosing a fluid status of a patient includes non-invasively determining a left ventricular pressure of blood within a left ventricle of a heart of the patient. The left ventricular pressure is compared to a predefined pressure value to diagnose the fluid status.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/978,111, filed Dec. 23, 2010, which is a divisional of U.S. patentapplication Ser. No. 11/166,600, filed Jun. 24, 2005, now U.S. Pat. No.7,857,769, which claims the benefit of U.S. Provisional Application No.60/682,280, filed May 18, 2005, which are hereby incorporated byreference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to the determination ofphysiological functions and parameters and more specifically to systemsand methods for non-invasively measuring left ventricular pressures ofthe blood within a left ventricle of a heart.

2. Description of Related Art

The function of the heart is well understood due in large part to theadvanced measurement techniques available to cardiologists and othermedical professionals. Many parameters of the cardiac cycle may bemeasured and monitored to determine the general well being of a patient.Some of the monitoring and measurement techniques are invasive,requiring sensors or other measurement devices to be placed within theheart or vessels connected to the heart, while other techniques arenon-invasive.

Some of the most important parameters associated with the cardiac cycleare pressures within the left ventricle of the heart. The left ventricleis the chamber of the heart responsible for pumping oxygenated bloodthroughout the body. The walls of the left ventricle act much like aspring: the more the walls are stretched, the more force the walls mayimpart to the blood when the ventricle contracts. For example, a normalventricle is able to expel about 70 mL of blood with a single strokeafter being stretched with a pressure (inside the ventricle) of about 10mmHg. If the walls of the ventricle are under-stretched, the heartdelivers less blood when the ventricle contracts. This may happen, forexample, when a person has bled so much that the volume of blood left inthe body is inadequate to properly fill the heart. The blood pressurethen drops significantly since the heart cannot pump out a sufficientamount of blood. Another example is when a person experiences myocardialinfarction. These “heart attacks” will sometimes cause a significantportion of the heart to die, and the remaining portion of the heart mustcompensate for the dead areas to keep the person alive. This oftenrequires that the blood coming into the ventricle stretch the ventriclewith more force than normal in order to get the normal amount of flow.In this particular instance, a pressure of 20 mmHg may be required tostretch the left ventricle enough in order to pump the same 70 mL ofblood with each stroke.

Several heart-related conditions are directly linked to pressures ofblood within the heart. When the heart requires an inordinate fillingpressure to pump the same amount of blood that usually would take only10 mmHg pressure, the patient is considered to have congestive heartfailure (CHF). If the heart cannot pump an adequate amount of blood, thepatient's blood pressure will fall. However, if the pressures in theleft ventricle exceed a certain point, then the blood may back into thelungs, thereby forcing blood and other fluids into the airspaces of thelungs. Under these circumstances, the patient is literally drowning.This condition is commonly referred to as pulmonary edema.

A patient may also have problems that are not heart related that exhibitsimilar symptoms to those caused by pulmonary edema. For example, fluidin the lungs may also be caused by the kidneys holding excess water, theliver not functioning properly, or the lining of the lungs beingdamaged, as in the case of drowning victims. When patients are examinedin the hospital, it is often impossible to just look at the patient anddetermine what the problem is.

Heart problems causing symptoms such as those described above may bemore easily diagnosed if the filling pressures of the heart are known.When the filling pressures of the heart are high, the heart is likely atfault. If the filling pressures are low, then the heart is usually avictim of other problems. The filling pressure, also referred to as theleft ventricular end-diastolic pressure (LVEDP), is the pressure ofblood within the left ventricle of the heart immediately followingdiastole (i.e. the filling cycle of the left ventricle) and beforesystole (i.e. when the left ventricle contracts to pump blood throughthe body).

There are primarily two procedures that have been used by physicians toobtain information about pressures within the heart. Both are forms ofcatheterization, but one approaches the heart from the left side and theother from the right. In a typical “left-heart catheterization,” aneedle is inserted in the groin, followed by a long flexible tube, thecatheter, which is advanced to the heart through a series of bloodvessels. The catheter finally passes into the large vessel known as theaorta on the downstream side of the left ventricle. The left-heartcatheterization is performed in a specialized lab by a trainedcardiologist, who uses special infusible dyes to make parts of the heartvisible. A left-heart catheterization provides a means of directlymeasuring pressure and flow in the heart. This is also the techniqueused to outline the coronary arteries and determine whether there is ablockage in the arteries in need of a bypass or balloon angioplasty.

In a “right-heart catheterization,” a long flexible tube called aSwan-Ganz catheter, is inserted in the neck or under the clavicle and isadvanced into the right side of the heart. The pressures that are mostdesired by physicians are those pressures within the left side of theheart, and blood leaving the right side of the heart must travel to thelungs before returning to the left side of the heart. The cathetertherefore includes a balloon attached to its tip, and the balloon isinflated with a small amount of air to allow the catheter to floatthrough the right atrium and right ventricle into the pulmonary artery.The catheter continues to move through the pulmonary artery until itwedges within a distal branch of the pulmonary artery that is smaller indiameter than the balloon. Since the balloon blocks blood flow throughthe small vessel in which it is wedged, a static column of blooddevelops between the tip of the catheter and the left atrium. In theory,the pressure measured within this static column of blood upstream of thelungs (i.e. the “wedge pressure”) approximates the left atrial pressure.If no obstruction exists between the left atrium and the left ventricle,the wedge pressure may also be a good approximation for the LVEDP. Mostof the time, these pressure approximations are accurate enough to allowdecisions to be made in the management of critically ill patients.

Left-heart catheterization requires a patient to be very stable, whileright-heart catheterization may be performed on critically ill patients.Right-heart catheterization is typically performed in the intensive careunit (ICU), the operating room, or in the emergency room, and isconducted by a specially trained physician. The procedure furtherrequires constant monitoring of heart and lung function, and thecatheter may only remain in place for one or two days due to the risk ofinfection and trauma to the heart. The placement of the Swan-Ganzcatheter alone may cost up to two thousand dollars.

Although the information provided by Swan-Ganz catheters is desperatelyneeded, the use of these catheters has fallen out of favor withphysicians during the last five years. The procedures are performed muchless frequently due to recent studies that suggest the catheters maycontribute to complications in patients. Even taking into account theserious illness of patients requiring a Swan-Ganz catheter, the act ofusing the catheter seems to increase the morbidity and mortality ofpatients. However, these procedures are still performed when there is noother choice.

A need therefore exists for a system and method that would allowphysicians to quickly and accurately determine the condition of apatient's heart without subjecting the patient to the dangers and risksof catheterization. A system is further needed that would allow thehealth of a patient's heart to be determined in a non-invasive mannerthat does not require physical penetration of the patient's skin orblood vessels. More specifically, a need exists for a system and methodthat would inexpensively allow determination of left ventricularpressures within the heart using non-invasive measuring techniques.

SUMMARY

The problems presented by determining left ventricular pressures withinthe heart are solved by the systems and methods of the illustrativeembodiments described herein. In one embodiment, a method of diagnosinga fluid status of a patient is provided. The method includesnon-invasively determining a left ventricular pressure of blood within aleft ventricle of a heart of the patient. The left ventricular pressureis compared to a predefined pressure value to diagnose the fluid status.

In another embodiment, a fluid status diagnostic system includes asensing unit configured to non-invasively measure a plurality of cardiacparameters of a left ventricle of a patient. The cardiac parametersinclude a mitral valve area and at least one of a stroke volume of theleft ventricle, a left ventricular diastolic filling time, a velocity ofblood entering the left ventricle, a maximum velocity of blood enteringthe left ventricle, and a change in velocity of blood entering the leftventricle over time. The system further includes a processor that isconfigured to receive the plurality of cardiac parameters and calculatea left ventricular pressure using the measured cardiac parameters. Theprocessor compares the left ventricular pressure to a predefinedpressure value to assist in the diagnosis of a fluid status.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a graph having a voltage profile, velocity profile,and pressure profile of a normal heart during diastole;

FIG. 2 depicts a graph having a sine wave used to model an E-phase of acardiac cycle;

FIG. 3 illustrates a flowchart detailing a method for measuring a leftventricular end-diastolic pressure according to an illustrativeembodiment;

FIG. 4 depicts a flowchart detailing a method for performing real-timemeasurements of a left ventricular pressure according to an illustrativeembodiment;

FIG. 5 illustrates a flowchart detailing a method for diagnosing acardiac function of a heart according to an illustrative embodiment;

FIG. 6 depicts a flowchart detailing a method for determining a fluidstatus of a patient according to an illustrative embodiment; and

FIG. 7 illustrates a schematic of a cardiac pressure monitoring systemaccording to an illustrative embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific illustrativeembodiments. These embodiments are described in sufficient detail toenable those skilled in the art to practice the illustrativeembodiments, and it is understood that other embodiments may be utilizedand that logical mechanical, electrical, and software changes may bemade without departing from the spirit or scope of the invention. Toavoid detail not necessary to enable those skilled in the art topractice the illustrative embodiments, the description may omit certaininformation known to those skilled in the art. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

The systems and methods of the present invention determine leftventricular pressures by non-invasively measuring certain cardiacparameters associated with a heart. The cardiac parameters may bemeasured at various times throughout the cardiac cycle of the heartdepending on the particular pressure of interest. For example, in atleast one embodiment, the left ventricular end-diastolic pressure(LVEDP) is determined, which is the pressure of blood within the leftventricle at the end of diastole and just prior to systole. Thispressure is also commonly referred to as the filling pressure, and asdescribed previously, represents an important value for determining theoverall health of the heart, and more specifically for determiningwhether the failing heart of a patient is being caused by non-cardiacissues or whether the heart itself is the root of the patient's problem.

The determination of LVEDP according to an illustrative embodiment isbased on the concept of momentum, especially the momentum of blood as itmoves into and through the left ventricle. Two equations may be derivedto determine an instantaneous pressure within the left ventricle at theend of diastole. The first equation (Equation 1) is based on theprinciple of momentum, and is derived by considering the typicalvelocity profile across the mitral valve. Referring to FIG. 1 in thedrawings, a typical velocity profile 111 during diastole across themitral valve is illustrated. During diastole, the velocity across themitral valve peaks twice, the first peak corresponding to the E phase ofthe cardiac cycle (i.e. an E phase peak 113) and the second peakcorresponding to the A phase (i.e. an A phase peak 115). Alsoillustrated in FIG. 1 is a voltage profile 121 and a pressure profile131. Each of the profiles 111, 121, 131 in FIG. 1 are illustrated as afunction of time (t), and the profiles are aligned with respect todiscrete times during the cardiac cycle. For example, when the velocityprofile peaks at the E phase peak 113, it is evident that thecorresponding pressure is at a substantially minimum value. The pressureat this particular time corresponds to the LVEDP. The majority of theblood filling the left ventricle occurs during the E phase. During thelater A phase, much less is contributed to the development of thefilling pressure. Consequently, the majority of the filling pressure(LVEDP) develops in approximately the first one third (⅓) of the fillingtime (i.e. diastole).

Referring now to FIG. 2, the velocity profile during diastole may bemodeled as a sine function, represented by a sine wave 211. Since theLVEDP develops during the E phase, it is the E phase that is modeled.The E phase is represented on the sine wave 211 by a primary region 215shown in a solid line and a secondary region 217 shown in a broken line.The velocity profile represented by the primary region 215 of the sincewave 211 includes a maximum velocity, ν_(max). The primary region 215spans a time period A that is approximately ⅓ of diastole, whichcorresponds to the amount of time occupied by the E phase. A time periodB is representative of the sine wave period, T. A time period C isrepresentative of the total filling time, or diastole.

Mathematically, the primary region 215 of the sine wave 211 may berepresented by the following velocity equation:

v=v _(max) sin(ωt).

The angular frequency, ω, is represented by:

${\omega = \frac{2\pi}{T}},$

where T is the period (see time period B in FIG. 2). Since the E phaseand the development of the filling pressure occurs during the firstthird of the diastolic filling time, t_(D), (see time period C in FIG.2), it is this first third that is of interest in determining LVEDP.Therefore, since the E phase corresponds to only half of a completeperiod of the sine wave (see time period A in FIG. 2), the period may bedetermined as follows:

$T \approx {\frac{2\Delta \; t_{D}}{3}.}$

To determine the LVEDP, the equations for velocity are used with thefollowing equation for momentum:

p=mv.

where p is the momentum, m is the mass, and v is the velocity. The forceequation, in terms of momentum is:

$F = {\frac{p}{t} = {{m\frac{v}{t}} + {v{\frac{m}{t}.}}}}$

Since the velocity of the blood is zero (i.e. v=0) at the time at whichLVEDP is determined, the force equation becomes:

$F = {m{\frac{v}{t}.}}$

Taking advantage of the velocity profile developed above, the derivativeof the velocity equation yields dv/dt:

v = v_(max)sin (ω t), and$\frac{v}{t} = {\omega \; v_{\max}{\cos \left( {\omega \; t} \right)}}$

Now, the equation for force may be more specifically written as:

F=mωv _(max) cos(ωt).

Substituting for the angular frequency a and the period T yields:

$F = {\frac{3\pi \; {mv}_{\max}}{\Delta \; t_{D}}{{\cos \left( {3\pi} \right)}.}}$

Solving for the LVEDP yields Equation 1:

$\begin{matrix}{{{{L\; V\; E\; D\; P} = \frac{F}{A_{mitral}}},{and}}{{L\; V\; E\; D\; P} = {3\pi \; {\rho\left( {S\; V}\; \right)}{v_{\max}.}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Equation 1 has the advantage of using data that may be easily measuredand plugged into a calculator for an instant result. The second equationfor LVEPD may be similarly used to obtain instant hand calculations ofthis important pressure and is based more specifically on the concept ofimpulse, which is the difference in momentum at two different times.Like Equation 1, the calculation of Equation 2 takes advantage of thefact that the flow across the mitral valve of the heart reaches a peak,and then falls off to zero at the precise moment for which it is desiredto obtain the LVEDP. The impulse equation is represented mathematicallyby the following equation:

Impulse=Δp=p ₂ −p ₁,

where p₁ is the momentum at a first time and p₂ is the momentum at asecond time. At the time the LVEDP is measured, since the velocity ofthe blood at the second time is zero, p₂ equals zero. The continuityequation is then used to relate the velocity of blood flow across themitral valve to the volume, V, of blood passing the mitral valve:

$v = \frac{\Delta \; V}{A_{mitral}\left( {\Delta \; t} \right)}$

where v is the velocity of the blood across the mitral valve, A_(mitral)is the area across the mitral valve, and Δt is the time over which thevolume change is measured.

The average force, F_(avg), exerted by the blood entering the leftventricle may be determined based on its relationship to the change inmomentum over time, as represented by the following equation:

$F_{avg} = {\frac{\Delta \; p}{\Delta \; t} = \frac{p_{2} - p_{1}}{\Delta \; t}}$

Since momentum is equal to the mass of an object (i.e. blood) multipliedby the velocity of the object, and since the term p₂ equals zero asexplained previously, the equation for average force may be rewrittenas:

${F_{avg} = \frac{{mv}_{\max}}{\Delta \; t}},$

where m is the mass of the blood and v_(max) is the maximum velocityacross the mitral valve during diastole. The equation for v_(max) maythus be rewritten as:

${v_{\max} = \frac{S\; V}{A_{mitral}\left( {\Delta \; t} \right)}},$

where SV is the stroke volume of the left ventricle. Substituting thisequation for v_(max) in the force equation and rewriting m in terms ofdensity, ρ, and stroke volume (i.e. m=ρ×SV) yields:

$F_{avg} = {\frac{\rho}{A_{mitra}}{\left( \frac{S\; V}{\Delta \; t} \right)^{2}.}}$

Solving for LVEDP yields:

${{L\; V\; E\; D\; P} = \frac{F_{avg}}{A_{mitral}}},{or}$${L\; V\; E\; D\; P} = {{\rho \left( \frac{S\; V}{A_{mitral}\left( {\Delta \; t} \right)} \right)}^{2}.}$

As mentioned previously, Δt is the time over which the volume change ismeasured. Referring again to FIGS. 1 and 2, the E phase, during whichthe LVEDP is developed, represents approximately ⅓ of the totaldiastolic filling time, t_(D). The calculation for Equation 2 involvesthe change in momentum between the time the velocity is zero and thetime the velocity is at a maximum (see v_(max) on FIG. 2). This maximumvelocity develops within about the first half the E phase, or ⅙ of thetotal diastolic filling time. Therefore, Δt may be represented as:

${{\Delta \; t} = \frac{\Delta \; t_{D}}{6}},$

and the LVEDP may be rewritten as:

$\begin{matrix}{{L\; V\; E\; D\; P} = {36{{\rho \left( \frac{S\; V}{A_{mitral}\left( {\Delta \; t_{D}} \right)} \right)}^{2}.}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

If metric values are used to calculate the LVEDP in Equations 1 and 2,the resultant pressure will be obtained in Pascals, which may beconverted to the units used in cardiology, mmHg, by multiplying by7.5006×10⁻³.

Once again, Equations 1 and 2 allow a physician or technician to readdata directly from a non-invasive measurement apparatus (e.g.echocardiogram apparatus, magnetic resonance imaging (MRI) apparatus,computer-aided tomography (CAT) apparatus, or any other non-invasivemeasurement apparatus) and then directly calculate the filling pressureusing a calculator. Software is not necessarily needed for performingthese calculations. However, these equations may be incorporated intothe firmware or software of the non-invasive measurement apparatus or acomputer or other processing system to allow automatic calculation ofthe filling pressure.

A third equation, also based on the principles of momentum, allowspressures within the left ventricle to be determined at any time duringthe cardiac cycle (not only at the end of diastole) based uponnon-invasive measurements conducted by a non-invasive measurementapparatus (e.g. an echocardiogram, an MRI, a CAT, or any other apparatusthat allows noninvasive measurements of cardiac parameters). Asmentioned previously, the momentum equation is represented by:

p=mv,

where p is the momentum, m is the mass, and v is the velocity. Force, F,may be written in terms of momentum:

$F = {\frac{p}{t} = {{m\frac{v}{t}} + {v\frac{m}{t}}}}$

Velocity, v, may be represented in terms of volume, V:

${v = {\frac{1}{A_{mitral}}\frac{V}{t}}},{and}$$\frac{v}{t} = {\frac{1}{A_{mitral}}\frac{^{2}V}{t^{2}}}$

The mass, m, of blood within the left ventricle may be calculated bymultiplying the density, ρ of the blood (approximately 1060 kg/m³) bythe volume. Solving the force equation for left ventricular pressure,LVP, in terms of volume of the left ventricle, V, yields:

${L\; V\; P} = {{\frac{\rho}{A_{mitral}^{2}}\left\lbrack {{V\frac{^{2}V}{t^{2}}} + \left( \frac{V}{t} \right)^{2}} \right\rbrack}.}$

By using the velocity equation developed earlier and substitutingvelocity terms for volume, the left ventricular pressure equation mayalso be represented as follows:

$\begin{matrix}{{L\; V\; P} = {{\frac{\rho \; V}{A_{mitral}}\frac{v}{t}} + {\rho \; {v^{2}.}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

If LVEDP is desired, the velocity term of the equation is eliminatedsince v is zero at the time the filling pressure, LVEDP, is calculated.Solving for LVEDP yields Equation 4:

${{L\; V\; E\; D\; P} = \frac{F}{A_{mitral}}},$

and then

$\begin{matrix}{{L\; V\; E\; D\; P} = {\left( \frac{\rho \; S\; V}{A_{mitral}} \right){\frac{v}{t}.}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Both Equations 3 and 4 require that the change in velocity over time(dv/dt) (i.e. the slope of the velocity, or acceleration) be determined,which would preferably be numerically determined using softwareassociated with the non-invasive measurement apparatus (i.e.echocardiograph, MRI, CAT, or other non-invasive measurement apparatus)or a separate computer or processing system. By using Equation 3, it ispossible to obtain real-time blood pressures within the left ventricleat any time during the cardiac cycle.

Referring to FIG. 3, a method 311 of measuring a left ventricularend-diastolic pressure of blood within a left ventricle of a patientaccording to an illustrative embodiment is illustrated. The method 311includes a step 313 of non-invasively measuring a plurality of cardiacparameters of the patient, including a stroke volume of the leftventricle, a mitral valve area, and a left ventricular diastolic fillingtime. Each of the cardiac parameters is capable of being measurednon-invasively, or without physical penetration of the skin or bloodvessels of the patient, by an echocardiograph, MRI, CAT, or othermeasurement apparatus. Echocardiography is the preferred method ofmeasurement since it is less expensive than MRI and CAT techniques. Bydirecting sound waves into a target area of the body (e.g. the leftventricle of the heart) and then capturing the sound waves after beingreflected from the target area, the echocardiograph is able to image thetarget area based on the varying densities of different tissues withinthe target area. The images developed by the echocardiograph during thecardiac cycle allow determination of the volumes of heart chambers atvarious times throughout the cardiac cycles (e.g. the stroke volume ofthe left ventricle), areas of openings between chambers (e.g. the mitralvalve area), and time periods associated with the cardiac cycle (i.e.the left ventricular diastolic filling time). If a Dopplerechocardiograph is used, the velocity of blood entering the leftventricle, including the maximum velocity of blood entering the leftventricle, may also be measured. The measurement of these types ofcardiac parameters may also be easily accomplished using the imagingtechniques provided by MRI and CAT.

The method 311 also includes a step 315 of calculating the leftventricular end-diastolic pressure using the measured cardiacparameters. One method of calculating the LVEDP is to use eitherEquation 1 or Equation 2 described previously because of the simplicityof hand calculation. If real-time pressures are being monitored, thepressure within the ventricle at any time or the LVEDP may be calculatedusing Equation 3. Equation 4 may also be used to calculate LVEDP. Whilethe specific cardiac parameters used in each of these equations variesslightly, all equations will give a good indication of the LVEDP. Theactual process of calculating the LVEDP may be performed manually, bycalculator, or by a firmware or software program. If a firmware orsoftware program is used, the program may be integrated into thenon-invasive measurement apparatus used to measure the cardiacparameters, or the program may be independently stored and/or operatedby a separate computer or processing system such as a personal computeror a handheld device.

Referring to FIG. 4, a method 411 for performing real-time measurementsof a left ventricular pressure of blood within a left ventricle of apatient is illustrated according to an illustrative embodiment. Themethod 411 includes a step 413 of non-invasively measuring a pluralityof cardiac parameters, including without limitation a stroke volume ofthe left ventricle and a mitral valve area. Each of the cardiacparameters is capable of being measured non-invasively by anechocardiograph, MRI, CAT, or other measuring apparatus. Theechocardiograph is the preferred method of measurement since it is lessexpensive than MRI and CAT techniques.

In another step 415 of the method 411, a change in velocity of the bloodentering the left ventricle over time is monitored. In Equations 3 and4, the change in velocity of the blood over time is represented by thederivative dv/dt. This parameter may also be referred to as the “slope”of the velocity or the acceleration of blood through the left ventricle.This parameter of the heart may be measured using Dopplerechocardiography, MRI, CAT or other measurement techniques fordetermining cardiac blood velocities.

The method 411 further includes a step 417 of determining the leftventricular pressure of the blood using the measured cardiac parametersand the change in velocity over time. The left ventricular pressure maybe the pressure of the blood in the left ventricle at any time duringthe cardiac cycle. For example, this may include the LVEDP measured atthe end of diastole, or it may be a pressure measured during systole.These pressure determinations are preferably made in real-time byapplying Equation 3 to the cardiac parameters measured at a given timeduring the cardiac cycle and the slope of the velocity. Since aderivative is involved in Equation 3, it is preferred that the leftventricular pressures are determined using a software or firmwareprogram that is programmed to include Equation 3 or a variation ofEquation 3. The program may be integrated into the non-invasivemeasurement apparatus used to measure the cardiac parameters, or theprogram may be independently stored and/or operated by a separatecomputer or processing system such as a personal computer or a handhelddevice. If only the LVEDP is sought, then Equation 4 may be used in lieuof Equation 3.

Equation 3 allows measurement of pressures within the left ventricle atany time during the cardiac cycle. This capability allows the pressuresto be displayed in real-time as cardiac parameters are being measured.This additional data is useful to physicians in obtaining a completepicture of the heart during the cardiac cycle.

Referring to FIG. 5 in the drawings, a method 511 of non-invasivelydiagnosing a cardiac function of a patient according to an illustrativeembodiment is illustrated. “Cardiac function” is used generally hereinto describe the condition of the heart as it relates to identifyingwhether or not the heart is experiencing problems. Cardiac function isnot meant to be used in a limiting sense and the diagnosis of a cardiacfunction may refer to identifying a heart-related problem or condition,including without limitation angina, myocardial infarction, CHF, or anyother heart-related problem, by non-invasively measuring pressuresassociated with the heart or vessels surrounding the heart. Thediagnosis of a cardiac function may also refer to the determination thatno heart-related problem exists.

There are a myriad of heart-related conditions that may be diagnosed ifpressures within the left ventricle, especially the LVEDP, aredetermined. The illustrative embodiments described herein are believedto aid in the diagnosis of cardiac function and in the cause of commonchest pain. One of the most challenging and costly evaluations in theemergency room today is determining the cause of chest pain. Angina,which manifests through a sensation of severe pain and constriction inthe chest, is caused by a temporary obstruction (due to constriction,clot formation, or plaque formation) of a blood vessel leading to theheart during periods of peak oxygen demand. This restriction results ina temporary deficiency of oxygen to the heart muscle served by theobstructed vessel. Myocardial infarction involves a complete cessationof blood flow to an area of the heart, which starves that particulararea of oxygen, thereby rendering the heart muscle in that area uselessif the supply of oxygen-carrying blood is not restored quickly.Myocardial infarction is what is commonly referred to as a “heartattack” and may result in serious illness or the death of the patient.

Congestive heart failure (CHF), while not presenting as chest pain, mayresult directly from a myocardial infarction. In CHF, the heart isunable to provide an adequate blood supply to the body with normalfilling pressures. Typically the contractility of the left ventricledecreases enough that it is unable to “squeeze” hard enough toadequately circulate blood throughout the body. The decreasedcontractility of the ventricle causes small volume increases in theventricle to produce relatively large pressure increases. These pressureincreases make the LVEDP an excellent determinant of CHF. When thepressures within the ventricle increase substantially, blood may pool inthe lungs causing pulmonary edema.

When attempting to diagnose chest pain, great difficulty lies indifferentiating between heart-related problems (e.g. angina, myocardialinfarction, and other causes of chest pain) and problems originatingelsewhere in the body. Angina and myocardial infarction may sometimes bediagnosed by reviewing a patient's heart rhythm on an electrocardiogrammachine, due to voltage differences in the patient's cardiac cycle.However, some patients, especially those with diabetes and hypertension,exhibit almost identical electrocardiographs regardless of whether thepatient is experiencing angina, myocardial infarction, or no heartproblems. For all patients experiencing chest pain, blood tests must beperformed to confirm heart-related problems. Evidence of angina ormyocardial infarction typically takes about six to eight hours tomanifest itself within the blood, and the tests are repeated three timesto ensure results. This extended delay in diagnosing and treatingpatients puts the patient at extreme risk of permanent heart damage ordeath. This also significantly increases the cost of diagnosis to thepatient that has no heart problem.

Referring still to FIG. 5, the method 511 of diagnosing the cardiacfunction of a heart includes a step 515 of non-invasively determining aleft ventricular pressure within a left ventricle of the heart. The leftventricular pressure may be the LVEDP calculated by any of Equations 1through 4. The step 515 of determining the left ventricular pressure maybe accomplished by non-invasively measuring a plurality of cardiacparameters of the patient, which may include a stroke volume of the leftventricle, a mitral valve area, and a left ventricular diastolic fillingtime. Each of the cardiac parameters is capable of being measurednon-invasively, or without physical penetration of the skin or bloodvessels of the patient, by echocardiography, MRI, CAT, or othermeasurement techniques. Echocardiography is the preferred method ofmeasurement since it is less expensive than MRI and CAT. By directingsound waves into a target area of the body (e.g. the left ventricle ofthe heart) and then capturing the sound waves after being reflected fromthe target area, the echocardiograph is able to image the target areabased on the varying densities of different tissues within the targetarea. The images developed by the echocardiograph during the cardiaccycle allow determination of the volumes of heart chambers at varioustimes throughout the cardiac cycles (e.g. the stroke volume of the leftventricle), areas of openings between chambers (e.g. the mitral valvearea), and time periods associated with the cardiac cycle (i.e. the leftventricular diastolic filling time). If a Doppler echocardiograph isused, the velocity of blood entering the left ventricle, including themaximum velocity of blood entering the left ventricle, may also bemeasured. The measurement of these types of cardiac parameters may alsobe easily accomplished using the imaging techniques provided by MRI andCAT.

After determining the necessary cardiac parameters, the left ventricularpressure is calculated. If LVEDP is desired for the diagnosis,calculations may be accomplished with any of Equations 1, 2, 3, or 4.One method of calculating LVEDP is to use either Equation 1 or Equation2 because of the simplicity of hand calculation. While the specificcardiac parameters used in each of these equations varies slightly, allequations will give a good indication of the LVEDP. If real-timepressures are being monitored, the pressure within the ventricle at anytime may be calculated using Equation 3. The process of calculating theLVEDP or the other pressures within the ventricle may be performedmanually, by calculator, or by a firmware or software program. If afirmware or software program is used, the program may be integrated intothe non-invasive measurement apparatus used to measure the cardiacparameters, or the program may be independently loaded on a separatecomputer or processing system such as a personal computer or a handhelddevice.

The method 511 further includes a step 517 of comparing the leftventricular pressure to a pre-defined pressure value to diagnose thecardiac function. As previously explained, diagnosis of the cardiacfunction of the heart describes the process of determining the health ofthe heart, and more specifically, determining if any heart-relatedproblems are present.

When a region of the heart lacks oxygen due to angina or myocardialinfarction, the heart suffers at least temporary failure. The region ofthe heart that lacks an adequate blood supply (referred to as ischemia)does not pump, thereby leaving a larger burden on the part of the heartthat is still healthy. When the ischemic region of the heart is on theleft side of the heart, the LVEDP will typically increase. This is dueat least in part to the continued normal operation of the right side ofthe heart. As the right side continues to pump blood into the left sideof the heart, the ischemic region on the left side of the heart cannotmaintain normal pumping capability, which results in a buildup of bloodand thus pressure within the left chambers of the heart. When theischemic region of the heart is on the right side of the heart, theLVEDP will typically decrease. Since the right side of the heart is nolonger pumping at full capacity, the left side of the heart receivesless blood from the right side, thereby resulting in a pressure drop inthe left chambers of the heart. Typically, infarctions on the right sideof the heart are much less common than infarctions on the left side ofthe heart.

A healthy heart typically produces an LVEDP of about 10-15 mmHg (a“normal pressure range”). In the method 511 of one embodiment, thepre-defined pressure value may be a particular pressure value, or may bea range of values. For example, the pre-defined pressure value may bethe normal pressure range. If the LVEDP had been determined, it wouldthen be compared to the normal pressure range. If the LVEDP is betweenabout 10-15 mmHg, the diagnosis would most likely be that the patient isnot experiencing heart-related problems and that the current health ofthe heart is good. If the LVEDP is above about 15 mmHg, the heart ismost likely experiencing angina, myocardial infarction, or congestiveheart failure. If the LVEDP is below about 10 mmHg, the most likelydiagnosis is that a problem elsewhere in the body is affecting theoperation of the heart. However, in some cases, the determination of anLVEDP below 10 mmHg may be an indication that a myocardial infarction orother heart-related problem is occurring in the right side of the heart.The ranges and values for the pre-defined pressure value may of coursebe adjusted depending on the particular medical history and physicalcharacteristics of the patient.

Preliminary verification that the method 511 may be used to diagnosechest pain has yielded favorable results. An emergency room patient whohad previously been diagnosed with angina was non-invasively measuredusing an echocardiogram. The cardiac parameters measured included thestroke volume, the mitral valve area, the maximum velocity, and thediastolic filling time. When the patient was pain free, the LVEDP wascalculated to be about 16 mmHg, or close to a normal value. During twodifferent episodes of chest pain, the LVEDP was calculated to beapproximately 25 mmHg, thereby indicating angina.

Referring to FIG. 6, a method 611 of non-invasively diagnosing a fluidstatus of a patient according to an illustrative embodiment isillustrated. The diagnosis of the “fluid status” of a patient refersgenerally to determining the health of the patient with respect to fluidamounts (e.g. volumes) and fluid distributions in the body of thepatient. Fluid status is not meant to be used in a limiting sense andthe diagnosis of a fluid status may refer to identifying anyfluid-related problem or imbalance in the body, including withoutlimitation dehydration, sepsis, pulmonary edema, low blood volume, andshifts in intravascular fluid volumes, such as those caused by extensiveburns or trauma. Determining the fluid status may also be used tomonitor dialysis patients since removal of too much water from the bloodmay present serious complications. The diagnosis of a fluid status mayalso refer to the determination that no fluid-related problem exists.

The method 611 of non-invasively diagnosing a fluid status of a patientincludes a step 615 of non-invasively determining a left ventricularpressure within a left ventricle of the heart. The left ventricularpressure may be the LVEDP calculated by any of Equations 1 through 4.The step 615 of determining the left ventricular pressure may beaccomplished by non-invasively measuring a plurality of cardiacparameters of the patient, which may include a stroke volume of the leftventricle, a mitral valve area, and a left ventricular diastolic fillingtime. Each of the cardiac parameters is capable of being measurednon-invasively, or without physical penetration of the skin or bloodvessels of the patient, by echocardiography, MRI, CAT, or any othermeasurement techniques. Echocardiography is the preferred method ofmeasurement since it is less expensive than MRI and CAT techniques. Bydirecting sound waves into a target area of the body (e.g. the leftventricle of the heart) and then capturing the sound waves after beingreflected from the target area, the echocardiograph is able to image thetarget area based on the varying densities of different tissues withinthe target area. The images developed by the echocardiograph during thecardiac cycle allow determination of the volumes of heart chambers atvarious times throughout the cardiac cycles (e.g. the stroke volume ofthe left ventricle), areas of openings between chambers (e.g. the mitralvalve area), and time periods associated with the cardiac cycle (i.e.the left ventricular diastolic filling time). If a Dopplerechocardiograph is used, the velocity of blood entering the leftventricle, including the maximum velocity of blood entering the leftventricle, may also be measured. The measurement of these types ofcardiac parameters may also be easily accomplished using the imagingtechniques provided by MRI and CAT.

After determining the necessary cardiac parameters, the left ventricularpressure is calculated. If LVEDP is desired for the diagnosis,calculations may be accomplished with any of Equations 1, 2, 3, or 4.One method of calculating LVEDP is to use either Equation 1 or Equation2 because of the simplicity of hand calculation. While the specificcardiac parameters used in each of these equations varies slightly, allequations will give a good indication of the LVEDP. If real-timepressures are being monitored, the pressure within the ventricle at anytime may be calculated using Equation 3. The process of calculating theLVEDP or the other pressures within the ventricle may be performedmanually, by calculator, or by a firmware or software program. If afirmware or software program is used, the program may be integrated intothe non-invasive measurement apparatus used to measure the cardiacparameters, or the program may be independently stored and/or operatedby a separate computer or a processing system such as a personalcomputer or a handheld device.

The method 611 further includes a step 617 of comparing the leftventricular pressure to a pre-defined pressure value to diagnose thefluid status of the patient. As previously explained, diagnosis of thefluid status of the patient describes the process of determining thehealth of the patient with respect to fluid amounts and distributions inthe body, and more specifically determining if any fluid-relatedproblems are present.

Fluids exist throughout the body and may be categorized as intravascularfluids, interstitial fluids, and intracellular fluids. Intravascularfluids are those fluids within the circulatory vessels of the body suchas the blood vessels. Intracellular fluids are those fluids locatedwithin the cells of the body. Interstitial fluids are those fluids thatare not otherwise characterized as intravascular fluids or intracellularfluids. A major component of almost all fluids in the body is water.

Certain problems or occurrences may cause a decrease in the fluid volumeof a patient. In most cases, a decrease in the volume of a body fluidwill cause the blood to lose water volume. For example, when a patienthas intestinal or kidney problems for an extended period of time,excessive diarrhea or urination will often result in dehydration, whichthen results in a loss of blood water volume. Dehydration may also occurif the patient experiences a high fever for an extended period of time.For a patient requiring dialysis, blood is circulated to filter outimpurities that cannot be removed by the patient's kidneys. Watervolumes in a dialysis patient typically increase significantly betweentreatments, sometimes enough that the patient's weight will increasegreatly. The dialysis process removes water from the patient, but it maybe difficult to predict how much water needs to be removed during anygiven treatment. Technicians estimate the amount of water that needs tobe removed and then monitor the patient's blood pressure during thedialysis process. As the water volume decreases in the patient, theblood pressure may fall rapidly. Determining when to stop removing watermay be very difficult, and a patient's blood water volume may rapidlydrop to a level that is not healthy for the patient.

Other fluid-related problems include sepsis. When an infection developswithin the blood of a patient, the blood vessels react by dilating. Thedilation of these vessels effectively increases the volume of the“container” in which the blood resides, which results in symptomsmimicking low blood volume.

A healthy heart typically produces an LVEDP of about 10-15 mmHg (a“normal pressure range”). In the method 611 of one embodiment, thepre-defined pressure value may be a particular pressure value, or may bea range of values. For example, the pre-defined pressure value may bethe normal pressure range. If the LVEDP has been determined, it may thenbe compared to the normal pressure range. If the LVEDP is between about10-15 mmHg, the diagnosis would most likely be that the patient is notexperiencing fluid-related problems. However, an LVEDP below about 10mmHg most likely indicates a fluid-related (non-heart related) problem.For the conditions described above, such as dehydration, sepsis, and lowblood volume, the decreased volume of blood returning to the heart causethe pressures in the left ventricle to drop. Although an LVEDP belowabout 10 mmHg may be an indication of a right-heart myocardialinfarction, the more likely diagnosis is a fluid-related problem,especially in the absence of chest pain. The ranges and values for thepre-defined pressure value may of course be adjusted depending on theparticular medical history and physical characteristics of the patient.

Referring now to FIG. 7, a cardiac pressure monitoring system 711according to an illustrative embodiment includes a computer or otherprocessing system 712 having a processor 713 operably connected to amemory medium 715, which may include RAM, ROM, or any other memorymedium. The processor 713 may be composed of one or more processors incommunication with each other. The computer 712 further includes astorage device 716 operably connected to the processor 713, the storagedevice 716 having at least one database 717 or data reservoir. Thestorage device may include a hard drive, magnetic media, optical media,or any other storage medium capable of storing data. The computer 712further includes at least one input/output device 718, such as akeyboard, a mouse, or a display monitor. A computer software program 720is operably associated with the processor 713 such that the instructionsof the computer software program 720 may be executed by the processor713. It should be noted that the computer software program 720 may bepermanently stored within storage device 716 and then at least partiallyloaded into memory medium 715 during operation of the computer 712. Thecomputer software program 720 would then be executed by the processor713, which communicates with the memory medium 715.

Preferably, the storage device 716 is capable of receiving and storing aplurality of non-invasively measured cardiac parameters associated witha left ventricle of a patient 719. The cardiac parameters are preferablymeasured by a sensing unit such as a sensor 725 associated with ameasuring apparatus 727 such as an echocardiograph, MRI, or CATapparatus. For example, the sensing unit may be a sonic transducer froman echocardiograph machine, or the sensing unit may be an RF receivercoil associated with an MRI machine. It is important to note that theterm sensing unit is not meant to be limiting and may include the sensoritself, the sensor and the associated hardware that are part of themeasuring apparatus, or any other sensing unit capable of measuring thecardiac parameters. The processor 713 may be used in conjunction withthe storage device 716 to manage the collection and storage of thecardiac parameters. Measuring apparatus 727 may include a monitor 731that is either integral to or separate from the measuring apparatus 727.The monitor 731 and/or the input/output device 718 may be used todisplay an output resulting from the methods discussed herein. Theoutput may include a single cardiac pressure, such as LVEDP, or mayinclude a plurality of cardiac pressures such as those that may bedetermined from a method similar to that illustrated in FIG. 4. Theoutput displayed may include a tabular or other type of listing ofcardiac pressure, or may include a graphical representation of thecardiac pressures similar to the pressure profile 131 of FIG. 1.

After receiving the cardiac parameters, the system 711 determines a leftventricular pressure by having the processor 713 calculate the pressureusing either Equation 1, 2, 3, or 4. The particular cardiac parametersthat are measured may depend on the equation that is used to calculatethe pressure. For example, if the left ventricular pressure at any giventime of the cardiac cycle is desired, Equation 3 may be used to generateand display real-time pressures within the left ventricle. If the leftventricular end-diastolic pressure is desired, any of the four equationsmay be used. For example, Equation 1 may be used in conjunction with themeasured cardiac parameters of stroke volume, mitral valve area, leftventricular diastolic filling time, and maximum velocity.

While the computer 712 may be integrated within any of the measuringdevices (e.g. echocardiograph apparatus, MRI apparatus, or CATapparatus) mentioned herein, it is also possible that the computer 712may be separately housed and electronically or wirelessly connected tothe measuring apparatus 727 as shown in FIG. 7. It is of course possibleto connect the computer 712 and/or the measuring apparatus 727 to anetwork 741, which may include without limitation a wide area network(WAN), a local area network (LAN), the Internet, or any other network.The network 741 would allow communication with other computing ordisplay devices 743 to allow remote monitoring or diagnosis of thepatient 719.

The system 711 of the present invention may also be used as a cardiacfunction diagnostic system to diagnose a cardiac function of the patient719 according to a method similar to method 511 illustrated in FIG. 5.If used as a cardiac function diagnostic system, the system 711 maymeasure a plurality of cardiac parameters with the sensing unit. Theprocessor 713 may receive the plurality of cardiac parameters, calculatea left ventricular pressure using the measured cardiac parameters, andcompare the left ventricular pressure to a predefined pressure value forassisting in the diagnosis of the cardiac function.

The system 711 of the present invention may also be used as a fluidstatus diagnostic system to diagnose a fluid status of the patient 719according to a method similar to the method 611 illustrated in FIG. 6.If the system 711 were used as a fluid status diagnostic system, aplurality of cardiac parameters may be measured by the sensing unit. Theprocessor 713 may receive the plurality of cardiac parameters, calculatea left ventricular pressure using the measured cardiac parameters, andcompare the left ventricular pressure to a predefined pressure value forassisting in the diagnosis of the fluid status of the patient 719.

Test Results

Preliminary test results for determining the LVEDP using Equation 1 haveproduced excellent results. The calculated pressure using non-invasivelymeasured cardiac parameters was compared with pressures obtained usingSwan-Ganz catheters. The data collected, measured, and calculated foreleven patients is illustrated in Table 1. Each wedge pressure wasmeasured using the Swan-Ganz catheter at approximately the same timethat the cardiac parameters were measured using non-invasive means.Patient 5 exhibited the only anomaly, but it is believed that valvestenosis may have contributed to the disparity in the wedge pressure andthe calculated pressure for this patient.

TABLE 1 CARDIAC PARAMETERS Calculated Wedge Stroke Mitral Valve FillingTime Peak Velocity LVEDP Pressure Patient Volume (ml) Area (cm³) (s)(m/s) (mmHg) (mmHg) 1 70 5.9 0.49 0.69 13 14 2 61 6 0.46 0.66 11 10 3 764 0.37 0.56 22 24 4 72 5 .035 0.6 19 17 5 45 1.1 0.55 0.77 43 23 6 755.5 0.44 0.6 14 16 7 72 5 0.4 0.75 20 19 8 55 3.9 0.38 0.8 22 22 9 69 50.45 0.6 14 13 10 73 3.9 0.44 0.65 21 23 11 80 5.5 0.31 0.77 27 24

The systems and methods of the present invention allow left ventricularpressures to be determined by non-invasively measuring selected cardiacparameters associated with a patient's heart. By using non-invasivemeasuring techniques such as echocardiography, Doppler echocardiography,MRI, and CAT to measure cardiac parameters such as the left ventricularstroke volume, the mitral valve area, the left ventricular diastolicfilling time, and the velocity of blood entering the left ventricle, thepressure of blood within the left ventricle may be determined.

Although many of the examples discussed herein are applicable to theleft ventricle of a human heart, the methods and systems of the presentinvention also may be applied to other chambers of the heart. In orderto determine other important values associated with the flow of bloodthrough the heart, the non-invasive measuring techniques would bedirected to the specific area of interest to determine cardiacparameters associated with that area. The principles of momentum may beadapted and applied to those areas of interest to determine pressures orother values that are not otherwise non-invasively obtainable. It shouldalso be noted that use of the systems and methods of the presentinvention is not limited to the left ventricles and hearts of humans,but also may be applied to other animals having blood flowcharacteristics that may be determined non-invasively. In this regard,the term “patient” used herein and throughout the claims may refer toeither a human or another animal for which cardiac pressuredetermination is desired.

While the systems and methods of determining left ventricular pressuresdescribed herein are well adapted to diagnosing the cardiac function andfluid status of a patient, the determination of left ventricularpressures may also be used to diagnose other problems (or lack ofproblems) experienced by a patient. It is contemplated that the systemsand methods may be used to diagnose any problems that would bedetectable by the use of a Swan-Ganz catheter or other invasiveprocedures used to determine cardiac pressures.

It should be apparent from the foregoing that an invention havingsignificant advantages has been provided. While the invention is shownin only a few of its forms, it is not just limited but is susceptible tovarious changes and modifications without departing from the spiritthereof.

1. A method of diagnosing a fluid status of a patient, the methodcomprising: non-invasively determining a left ventricular pressure ofblood within a left ventricle of a heart of the patient bynon-invasively measuring a plurality of cardiac parameters of thepatient, including a stroke volume of the left ventricle, a mitral valvearea, and a left ventricular diastolic filling time; and comparing theleft ventricular pressure to a predefined pressure value to diagnose thefluid status. 2-5. (canceled)
 6. The method according to claim 1,wherein the cardiac parameters are measured using one of anechocardiogram apparatus, a magnetic resonance imaging (MRI) apparatus,and a computer aided tomography (CAT) apparatus.
 7. A method ofdiagnosing a fluid status of a patient, the method comprising:non-invasively determining a left ventricular pressure of blood within aleft ventricle of a heart of the patient by non-invasively measuring aplurality of cardiac parameters of the patient, including a strokevolume of the left ventricle, a mitral valve area, and a leftventricular diastolic filling time; calculating a left ventricularend-diastolic pressure using a formula:${{L\; V\; E\; D\; P} = {36{\rho \left( \frac{S\; V}{A_{mitral}\left( {\Delta \; t_{D}} \right)} \right)}^{2}}},$where LVEDP is the left ventricular end-diastolic pressure, ρ is adensity of blood; SV is the stroke volume, A_(mitral) is the mitralvalve area, and Δt_(D) is the left ventricular diastolic filling time;and comparing the left ventricular pressure to a predefined pressurevalue to diagnose the fluid status.
 8. A method of diagnosing a fluidstatus of a patient, the method comprising: non-invasively determining aleft ventricular pressure of blood within a left ventricle of a heart ofthe patient by non-invasively measuring a plurality of cardiacparameters of the patient, including a stroke volume of the leftventricle, a mitral valve area, a maximum velocity of blood entering theleft ventricle, and a left ventricular diastolic filling time;calculating a left ventricular end-diastolic pressure using a formula:${{L\; V\; E\; D\; P} = \frac{3{{\pi\rho}\left( {S\; V} \right)}v_{\max}}{A_{mitral}\Delta \; t_{D}}},$where LVEDP is the left ventricular end-diastolic pressure, ρ is adensity of blood; SV is the stroke volume, v_(max) is the maximumvelocity of blood, A_(mitral) is the mitral valve area, and Δt_(D) isthe left ventricular diastolic filling time; and comparing the leftventricular pressure to a predefined pressure value to diagnose thefluid status.
 9. A method of diagnosing a fluid status of a patient, themethod comprising: non-invasively determining a left ventricularpressure of blood within a left ventricle of a heart of the patient bynon-invasively measuring a plurality of cardiac parameters, including avolume of the left ventricle, a velocity of blood entering the leftventricle, and a mitral valve area; monitoring a change in velocity ofthe blood entering the left ventricle over time; calculating the leftventricular pressure using a formula:${{L\; V\; P} = {{\frac{\rho \; V}{A_{mitral}}\frac{v}{t}} + {\rho \; v^{2}}}},$where LVP is the left ventricular pressure, ρ is a density of blood; Vis the volume of the left ventricle, A_(mitral) is the mitral valvearea, v is the velocity of blood entering the left ventricle, and$\frac{v}{t}$ is the change in velocity over time; and comparing theleft ventricular pressure to a predefined pressure value to diagnose thefluid status. 10-17. (canceled)